JP2011132566A - Desulfurization method for molten iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a desulfurization treatment with a desulfurization ratio equivalent to that achieved using a CaO-CaF<SB>2</SB>-based desulfurizing agent, by using a CaO-based desulfurizing agent containing no fluorine compound such as fluorite being a slagging intensifier of CaO. <P>SOLUTION: The desulfurizing agent is obtained by adding alumina-metallic Al mixture containing 10-50 mass% metallic Al to CaO powdery material in accordance with before-sulfurization temperature of the molten iron, namely adding the mixture to the CaO powdery material in the range of X mass% to X+15 mass%, wherein the X mass% is obtained by expression (2); X(mass%)=20 in the case of ≤1,250°C molten iron temperature, expression (3); X(mass%)=295-0.22×T in the case of >1,250°C to <1,340°C, and expression (4); X(mass%)=0.2 in the case of ≥1,340°C. The desulfurizing agent is added to the bath surface of the molten iron stirred with a stirring blade and thus, the molten iron is desulfurization-treated. Wherein, in the expression (3), T is the molten iron temperature (°C) before desulfurization treatment. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hot metal desulfurization method using a mechanical stirring desulfurization apparatus, and more particularly to a method for efficiently desulfurizing hot metal by promoting a desulfurization reaction.

  The hot metal discharged from the blast furnace contains high concentrations of phosphorus (element symbol: P) and sulfur (element symbol: S), which adversely affect steel quality, and various technologies have been developed to remove them. Has been. In today's steel refining process, a method of previously removing phosphorus and sulfur contained in hot metal prior to decarburization refining in a converter, so-called “pretreatment of hot metal” is generally performed. Among these, the hot metal desulfurization treatment holds the hot metal in a refining vessel having a substantially circular horizontal cross section, adds a desulfurizing agent onto the hot metal, and is called an impeller (also referred to as “stirring blade” or “stirring blade”). A method (hereinafter referred to as “mechanical stirring type desulfurization method”) in which a rotor having blades is immersed in hot metal and rotated, and the hot metal and the desulfurizing agent are stirred and desulfurized is widely used. In this mechanical stirring desulfurization method, an inexpensive desulfurization agent mainly composed of CaO (lime) is used.

The desulfurization reaction of molten iron with CaO is generally represented by the following formula (1).
[S] + (CaO) = (CaS) + [O] (1)
In the formula (1), [S] represents sulfur in the molten iron, (CaO) represents calcium oxide in the slag, (CaS) represents calcium sulfide in the slag, and [O] represents oxygen in the molten iron.

In this desulfurization treatment, conventionally, a fluorine compound such as fluorite (CaF ₂ ) has been used as an accelerator for CaO hatching. For example, CaO in which about 5% by mass of fluorite is mixed with quick lime as a CaO source. -CaF ₂ desulfurization agent have been widely used. However, in recent years, there is concern about the outflow of fluorine (F) to the environment from the viewpoint of global environmental protection, and it is desired to efficiently desulfurize without using a fluorine compound as a hatching accelerator for CaO.

As an example of a desulfurization agent that does not use a fluorine compound such as fluorite, a calcium carbide desulfurization agent and a soda desulfurization agent have been put into practical use, both of which have advantages and disadvantages. Calcium carbide-based desulfurization agents have a strong desulfurization ability, but there are safety problems such as the generation of acetylene gas in the post-treatment of the desulfurization slag after the desulfurization treatment. Moreover, since it is expensive and dangerous, it is extremely difficult to handle. A soda-based desulfurization agent is relatively inexpensive, but has a strong alkalinity, and thus has a great influence on the refractories of the processing furnace and the processing vessel. Further, since the exhaust gas contains Na, it is necessary to remove it. Furthermore, since the content of Na ₂ O in the slag is high, there is a restriction in the reuse to cement and the like, which is undesirable from the influence on the environment.

  Considering these, a desulfurization agent mainly composed of CaO is inexpensive and easy to handle. Therefore, even if it is a desulfurization agent mainly composed of CaO, a desulfurization agent that does not use a fluorine compound as a hatching accelerator. Has been proposed.

  For example, in Patent Document 1, 5 to 20 mass of an alumina-metal Al mixture containing 50 mass% or less of alumina with respect to 100 mass parts of CaO powder having a fine particle diameter of 150 μm or less of 90 mass% or more. A hot metal desulfurization agent characterized by the addition of a part thereof has been proposed. According to Patent Document 1, not only is the hatching accelerated by the alumina in the alumina-metal Al mixture added at the same time, but the aggregation of CaO is prevented by the alumina-metal Al mixture, and fluorite, etc. It is said that it can be efficiently desulfurized without using the fluorine compound as a hatching accelerator.

JP 2008-50659 A

  However, the above prior art has the following problems.

  That is, from the detailed investigation results of the present inventors, when a mixture of CaO powder and alumina-metal Al mixture as disclosed in Patent Document 1 is used as a desulfurization agent, the object of desulfurization treatment is used. It has been found that there is an optimum blending ratio of the alumina-metal Al mixture depending on the temperature of the hot metal. Specifically, when the hot metal temperature is low, in order to promote the hatching of CaO by the alumina-metal Al mixture, it is necessary to increase the blending ratio of the alumina-metal Al mixture, while the hot metal temperature is If it is high, it is necessary to lower the blending ratio of the alumina-metal Al mixture. Patent Document 1 does not disclose anything about this point.

The present invention has been made in view of the above circumstances. The object of the present invention is to contain a fluorine compound such as fluorite, which is a CaO hatching accelerator, in desulfurizing hot metal in a mechanical stirring desulfurization apparatus. By providing a desulfurization method for hot metal that can be efficiently desulfurized at a desulfurization rate equivalent to that obtained by using a conventional CaO-CaF ₂ desulfurization agent even if a CaO desulfurization agent that is not used is used. is there.

  The hot metal desulfurization method according to the first aspect of the present invention for solving the above problems is a hot metal desulfurization method using a mechanical stirring desulfurization apparatus, and contains 10 to 50% by mass of metal Al with respect to CaO powder. Range of X mass% or more and X + 15 mass% or less determined by the following formulas (2), (3) and (4) according to the temperature before desulfurization treatment of the hot metal to be desulfurized with the alumina-metal Al mixture The desulfurizing agent added in (1) is added to the bath surface of the hot metal being stirred by the stirring blade, and the hot metal is desulfurized.

Hot metal temperature: 1250 ° C or less X (mass%) = 20 (2)
Hot metal temperature: 1250 ° C and less than 1340 ° C X (mass%) = 295-0.22 x T (3)
Hot metal temperature: 1340 ℃ or higher X (mass%) = 0.2 (4)
However, in the formula (3), T is the hot metal temperature (° C.) before the desulfurization treatment.

  The hot metal desulfurization method according to the second invention is characterized in that, in the first invention, the desulfurizing agent is added by top blowing to the bath surface of the hot metal together with the conveying gas through the top blowing lance.

In the hot metal desulfurization method according to the third invention, in the second invention, the upper blow lance is arranged facing downward in the vertical direction, the inner wall radius of the processing container for containing the hot metal is D (m), When the horizontal distance from the center to the center of the upper blowing lance is A (m), the horizontal distance (A) satisfies the relationship of the following expression (5) with respect to the inner wall radius (D). It is characterized by being within.
0 ≦ A ≦ (2/3) × D… (5)

  According to the present invention, when performing hot metal desulfurization treatment using a mechanical stirring desulfurization apparatus, an alumina-metal Al mixture is added to a CaO powder at a predetermined blending ratio according to the hot metal temperature before treatment. Since the desulfurization treatment is performed using the added desulfurizing agent, not only CaO is accelerated by the alumina in the alumina-metal Al mixture added at the same time, but the desulfurization reaction is accelerated, and the alumina-metal Al mixture is also added. Therefore, the desulfurization agent cost can be suppressed. As a result, it is possible to efficiently desulfurize without using a fluorine compound such as fluorite as a hatching accelerator, and at the same time, the desired desulfurization treatment can be performed with a small amount of desulfurization agent, and the desulfurization agent basic unit is reduced. Reduction of the amount of generated slag accompanying this is achieved, and an industrially beneficial effect is brought about.

It is the schematic of the experimental apparatus which simulated the mechanical stirring desulfurization apparatus. It is a figure which shows the relationship between the desulfurization rate when hot metal temperature is 1300 degreeC, and the mixture ratio of the alumina- metal Al mixture of a desulfurization agent. It is a figure which shows the result of having measured the flow of the perpendicular direction in a bath, and its flow velocity value in a water model experiment apparatus. 1 is a schematic side view of a mechanical stirring desulfurization apparatus embodying the present invention.

  Hereinafter, the present invention will be specifically described. First, the background to the present invention will be described.

  The present inventors examined and studied means for efficiently desulfurizing hot metal by promoting the hatching of CaO and lowering the oxygen potential in the desulfurization treatment of hot metal using a mechanical stirring desulfurization apparatus.

  As a result, it was confirmed that the desulfurization rate was remarkably improved by desulfurization treatment using a desulfurization agent composed of a mixture of CaO powder and alumina-metal Al mixture as disclosed in Patent Document 1. did. This is the effect of increasing the interfacial area of desulfurization reaction by fine powder CaO, the effect of preventing aggregation of fine powder CaO by the alumina-metal Al mixture, and the effect of reducing the oxygen potential of hot metal by metal Al in the alumina-metal Al mixture. Is due to.

Here, as the alumina-metal Al mixture, aluminum dross (also referred to as “Al ash”) is optimal. Almidros is the stage of melting aluminum metal used in beverage recycling cans and automobile aluminum wheels, etc., in the stage of melting the aluminum metal in the recycling circuit, floating on the molten aluminum metal The metal Al is contained in an amount of 10 to 50% by mass, and the main component is a mixture of alumina and metal Al. Other components such as aluminum nitride are also contained because they are exposed to the air for a long time at a high temperature. The reason why the aggregation of fine CaO is prevented by the addition of the alumina-metal Al mixture is because the CaO-Al ₂ O ₃ based low melting point compound depends on the components other than alumina contained in the alumina-metal Al mixture. It is because formation of is suppressed.

  However, the present inventors have found from the results of desulfurization tests in actual machines that, in order to increase the desulfurization rate and efficiently desulfurize, the optimum mixing of both in the desulfurization agent composed of a mixture of CaO powder and alumina-metal Al mixture. It has been found that the ratio varies depending on the hot metal temperature. In recent years, desulfurization slag (desulfurization agent after desulfurization treatment) has been recycled as a cement material and a roadbed material. For these applications, it is desirable that the amount of alumina in the slag is small. From these events, it was concluded that efficient desulfurization treatment was required with the minimum amount of alumina-metal Al mixture added corresponding to the hot metal temperature.

  Therefore, the present inventors have further studied and studied in order to solve this problem. As an element to solve this problem, we examined and examined the quantification of the relationship between the optimum blending ratio of the alumina-metal Al mixture to the CaO powder and the hot metal temperature.

  In the test, an experimental apparatus simulating a mechanical stirring type desulfurization apparatus was used, and a desulfurization agent was sprayed and added to the hot metal bath surface using nitrogen gas as a carrier gas from an upper blowing lance, and the desulfurization behavior at that time was investigated. As a desulfurizing agent, an alumina-metal Al mixture containing about 30% by mass of metal Al is blended at a blending ratio of 0 to 50% by mass with CaO powder having a fine particle size of 150 μm or less of 90% by mass or more. Used. The hot metal temperature was tested in the range of 1150 to 1400 ° C. FIG. 1 shows a schematic diagram of an experimental apparatus simulating a mechanical stirring type desulfurization apparatus.

  The experimental apparatus is equipped with a high frequency heating coil 14, held in a crucible container 10 having an inner wall radius (D) of 150 mm, impregnated with impeller 12 in molten iron 3 heated and melted by high frequency heating coil 14, and impeller by electric motor 13. 12 was rotated and the hot metal 3 was stirred. After the molten iron 3 is in a steady state, the desulfurizing agent in which the mixing ratio of the alumina-metal Al mixture is adjusted in advance from the top blowing lance 11 installed above the bath surface of the molten iron 3 using nitrogen gas as the carrier gas. Was sprayed onto the hot metal bath surface. The installation position of the top blowing lance 11 was fixed at a position where the horizontal distance from the center position of the crucible container 10 was 80 mm.

  As a result, FIG. 2 shows a relationship between the desulfurization rate when the hot metal temperature is 1300 ° C. and the blending ratio of the alumina-metal Al mixture. It was found that when the body was blended, the desulfurization rate was saturated and did not change, or the desulfurization rate decreased. It was also found that the desulfurization rate decreased even when the amount of the alumina-metal Al mixture was small. That is, it has been found that there is an appropriate value for the blending ratio of the alumina-metal Al mixture in the desulfurizing agent according to the hot metal temperature during the desulfurization treatment. The desulfurization rate is a value defined by the following equation (6).

This is related to the liquid phase generation effect by the alumina-metal Al mixture, and when the mixing ratio is optimal, the liquid phase is uniformly generated and the desulfurization rate is improved. Has a small liquid phase generation effect and does not improve the desulfurization rate. On the other hand, when the blending ratio is too high, CaO particles are agglomerated by a large amount of the liquid phase, resulting in a small reaction interface area and desulfurization. This is because the rate decreases. Generally, low melting point CaO—Al ₂ O ₃ which is a reaction product of alumina and CaO is known to have a high viscosity, and CaO—Al ₂ O ₃ produced in a large amount causes aggregation of CaO. Because it goes.

  It was also found that when the mixing ratio of the alumina-metal Al mixture is the same, the desulfurization rate generally increases as the hot metal temperature increases.

  As a result of comprehensive analysis of these results, in the desulfurization agent composed of a mixture of CaO powder and alumina-metal Al mixture, in order to increase the desulfurization rate and efficiently desulfurize, the alumina-metal Al mixture The blending ratio of the body should be in the range of not less than X mass% and not more than “X + 15” mass% determined by the following formulas (2), (3) and (4) according to the hot metal temperature before the desulfurization treatment. I found out that

Hot metal temperature: 1250 ° C or less X (mass%) = 20 (2)
Hot metal temperature: 1250 ° C and less than 1340 ° C X (mass%) = 295-0.22 x T (3)
Hot metal temperature: 1340 ℃ or higher X (mass%) = 0.2 (4)
However, in the formula (3), T is the hot metal temperature (° C.) before the desulfurization treatment.

When the hot metal temperature is low, the CaO powder is difficult to hatch, so it is necessary to increase the blending ratio of the alumina-metal Al mixture. On the other hand, when the hot metal temperature is high, the CaO tends to hatch, so the alumina-metal Reduce the blending ratio of the Al mixture. In addition, when the hot metal temperature is high, the amount of low melting point CaO—Al ₂ O ₃ is increased by the addition of the alumina-metal Al mixture, which causes aggregation of CaO particles and decreases the reaction interface area. Therefore, in order to prevent this, the blending ratio of the alumina-metal Al mixture is lowered as the hot metal temperature becomes higher.

  The CaO powder used as the desulfurization agent is sufficient if the fine powder having a particle size of 150 μm or less is 90% by mass or more, and the alumina-metal Al mixture used as the desulfurization agent is made of metal Al as in the case of aluminum dross. If it contains 10-50 mass%, there is no problem.

  In addition, as a method of adding powder desulfurization agent with a good yield, a method of adding a desulfurization agent together with a carrier gas from the top blowing lance with a blowing lance as compared with the top addition method has a much higher yield. It was confirmed that the desulfurization rate was improved.

  Furthermore, from the test results in the actual machine, it was found that when the desulfurizing agent was added with the carrier gas via the upper blowing lance, the desulfurization rate varied greatly depending on the spraying position of the desulfurizing agent. As a result of various investigations of this cause, it was confirmed that the flow in the mechanical stirring bath had a great influence.

  Therefore, the flow in the bath at the time of mechanical stirring was quantitatively determined using a water model experimental apparatus of a mechanical stirring type desulfurization apparatus having an inner diameter of 150 mm. In the water model experimental apparatus, as a result of measuring the vertical flow and the flow velocity value at the time of mechanical stirring, as shown in FIG. 3, the horizontal distance from the container center is 100 mm, that is, 2/3 of the container radius. It was found that on the inner side, the flow on the bath surface and in the bath was downward, whereas on the outer side, the flow was upward.

  When the flow in the bath is downward, that is, when the desulfurizing agent is added by blowing up at a position within 2/3 of the radius of the vessel, the desulfurizing agent blown from the upper blowing lance enters the bath and then rides on the downward flow. When the desulfurization reaction proceeds while being entrained in the bath, when the flow in the bath is upward, that is, when the desulfurization agent is added by spraying at a position outside 2/3 of the vessel radius, the sprayed desulfurization agent is Once it enters the bath, it rides on the upward flow and floats on the bath surface, and the desulfurization reaction is suppressed.

That is, it has been found that when the upper blowing lance is arranged in the vertically downward direction, a high desulfurization rate can be obtained when the installation position of the upper blowing lance is within a range that satisfies the relationship of the following expression (5).
0 ≦ A ≦ (2/3) × D… (5)
However, in the formula (5), A is a horizontal distance (m) from the center of the processing container to the center position of the upper blowing lance, and D is an inner wall radius (m) of the processing container.

  The present invention is based on these test results. In the hot metal desulfurization method using a mechanical stirring desulfurization apparatus, the alumina-metal Al mixture containing 10 to 50% by mass of metal Al with respect to CaO powder. Desulfurizing agent added in the range of X mass% or more and X + 15 mass% or less determined by the above formulas (2), (3) and (4) according to the temperature before desulfurization treatment of hot metal to be desulfurized Is added to the bath surface of the hot metal being stirred by the stirring blade, and the hot metal is desulfurized.

  Next, the hot metal desulfurization method according to the present invention will be described with reference to the drawings.

  FIG. 4 is a schematic side view of a mechanical stirring desulfurization apparatus embodying the present invention, and FIG. 4 shows an example in which a pan-type hot metal ladle having a circular horizontal cross section is used as a processing container for containing hot metal. Yes. Regarding the shape of the processing vessel, since the desulfurization treatment is performed by a mechanical stirring type desulfurization apparatus, a processing vessel having a circular horizontal cross section as shown in FIG. 4 is optimal.

  In FIG. 4, a hot metal ladle 2 containing hot metal 3 discharged from a blast furnace is mounted on a carriage 1 and carried into a mechanical stirring desulfurization apparatus. The mechanical stirring type desulfurization apparatus is equipped with a refractory impeller 4 which is immersed and buried in a hot metal 3 accommodated in a hot metal ladle 2 and swirls to stir the hot metal 3. The impeller 4 is a lifting device. (Not shown) is moved up and down in a substantially vertical direction, and is rotated about a shaft 4a as a rotation axis by a rotating device (not shown). Further, in the mechanical stirring type desulfurization apparatus, an upper blowing lance 5 for adding the desulfurizing agent 6 by blowing it upward toward the hot metal 3 accommodated in the hot metal ladle 2 is disposed almost vertically below the hot metal 3. It is installed facing.

  The top blowing lance 5 is connected to a supply device including a dispenser 7 containing the powdered desulfurizing agent 6 and a cutting device 8 for quantitatively cutting out from the dispenser 7, and is transported from the tip of the top blowing lance 5. The powdered desulfurization agent 6 can be supplied together with the working gas at an arbitrary timing. As the carrier gas for the desulfurizing agent 6, a reducing gas such as hydrocarbon gas, hydrogen gas, and CO gas, an inert gas such as Ar gas, or a non-oxidizing gas such as nitrogen gas is used.

  In the present invention, the desulfurization agent 6 to be used differs in the blending ratio of the alumina-metal Al mixture depending on the temperature of the hot metal 3 before the desulfurization treatment. Therefore, a plurality of dispensers 7 are provided, for example, alumina-metal. Desulfurizing agents with different mixing ratios of alumina-metal Al mixture, such as 30 wt% desulfurizing agent, 20 wt% desulfurizing agent, 10 wt% desulfurizing agent, 5 wt% desulfurizing agent, etc. It is preferable to load 6 into each dispenser 7. In addition, two dispensers 7 are provided, the CaO powder is stored in one dispenser, the alumina-metal Al mixture is stored in the other dispenser, and the cut-out amount of both cut-out devices 8 is adjusted. The mixing ratio of the metal Al mixture may be controlled.

  Further, a dust collecting hood 9 that covers the hot metal ladle 2 is provided above the hot metal ladle 2, and exhaust gas and dust being processed are collected through an exhaust duct (not shown) attached to the dust collecting hood 9. (Not shown). In this case, the shaft 4a of the impeller 4 and the upper blowing lance 5 are installed so as to penetrate the dust collection hood 9 and move up and down.

  The position of the carriage 1 on which the hot metal ladle 2 is mounted is adjusted so that the position of the impeller 4 is substantially at the center of the hot metal ladle 2, and the hot metal temperature is measured by a temperature measuring device (not shown) such as a thermocouple. The impeller 4 is lowered and immersed in the hot metal 3. If the impeller 4 is immersed in the hot metal 3, the impeller 4 starts to turn and the speed is increased to a predetermined rotational speed. If the rotation speed of the impeller 4 reaches a predetermined rotation speed, the desulfurization agent, which is a blending ratio of the alumina-metal Al mixture according to the measured hot metal temperature determined by the above formulas (2) to (4) 6 is activated by spraying from the top blowing lance 5 toward the bath surface of the hot metal 3 together with the carrier gas by starting the cutting device 8. In this case, it is preferable that the position of the top blowing lance 5 satisfies the above formula (5).

  When the addition of a predetermined amount of the desulfurizing agent 6 is completed and stirring is performed for a predetermined time, the rotational speed of the impeller 4 is decreased and stopped. If the turning of the impeller 4 is stopped, the impeller 4 is raised and waited above the hot metal ladle 2. The generated desulfurization slag rises and covers the hot metal surface, and the desulfurization process of the hot metal 3 is completed in a stationary state. After the desulfurization treatment, the generated desulfurization slag is discharged from the hot metal ladle 2 and conveyed to the next refining process.

  By desulfurizing the hot metal 3 in this way, the CaO powder in the desulfurizing agent is promoted to hatch by the alumina in the alumina-metal Al mixture added at the same time, thereby promoting efficient desulfurization treatment. In addition, since the addition amount of the alumina-metal Al mixture does not become excessive, the desulfurization agent cost can be suppressed. Thereby, it is possible to efficiently desulfurize without using a fluorine compound such as fluorite as a hatching accelerator, and at the same time, it is possible to carry out a desired desulfurization treatment with a small amount of desulfurizing agent 6.

  Desulfurization of hot metal using a mixture of a CaO powder having a fine particle size of 150 μm or less and 90 mass% or more and an alumina-metal Al mixture as a desulfurization agent using the mechanical stirring desulfurization apparatus shown in FIG. The result (Invention Examples 1-8 and Comparative Examples 1-9) is shown.

  In both examples of the present invention and comparative examples, Al dross containing 10-30% by mass of metal Al is used as the alumina-metal Al mixture, nitrogen gas is used as the desulfurization agent transport gas, and four impellers are used. The blades with no inclination were used. The chemical components of the hot metal used were C: 3.5 to 5.0 mass%, Si: 0.1 to 0.3 mass%, P: 0.05 to 0.15 mass%, S: 0.04 to The hot metal temperature was in the range of 1200 to 1350 ° C. at 0.05 mass%. In the desulfurization treatment, a hot metal ladle having an inner wall radius of 2000 mm, which can treat 200 to 500 tons of hot metal, was used as a treatment container. The top blowing lance was installed at a position of distance A = (1/3) × D, and the addition amount per ton of molten CaO in the desulfurizing agent was constant in both the present invention example and the comparative example.

  In both the inventive example and the comparative example, samples were taken from the hot metal before and after the desulfurization treatment, and the desulfurization rate was investigated. The results of the examples of the present invention and comparative examples are shown in Table 1.

As shown in Table 1, in Examples 1 to 8 of the present invention, the desulfurization rate was as high as 87% or higher, whereas in Comparative Examples 1 to 7 and Comparative Example 9, the desulfurization rate was as low as 80% or less. . Further, as shown in Comparative Example 8, even when an alumina-metal Al mixture of a predetermined amount or more is added, the desulfurization rate is hardly changed as compared with Example 8, and the alumina-metal Al mixture is wasted. Was confirmed. In Comparative Example 9, the mixing ratio of the alumina-metal Al mixture is excessive, and the amount of low melting point CaO—Al ₂ O ₃ generated is increased, which causes aggregation of CaO particles, resulting in a reaction interface area. Decrease and desulfurization rate decreased.

DESCRIPTION OF SYMBOLS 1 Bogie 2 Hot metal ladle 3 Hot metal 4 Impeller 5 Top blowing lance 6 Desulfurizing agent 7 Dispenser 8 Cutting device 9 Dust collection hood 10 Crucible container 11 Top blowing lance 12 Impeller 13 Electric motor 14 High frequency heating coil

Claims (3)

In the hot metal desulfurization method using a mechanical stirring type desulfurization apparatus, an alumina-metal Al mixture containing 10 to 50% by mass of metal Al with respect to CaO powder depends on the temperature before desulfurization treatment of hot metal to be desulfurized. The desulfurizing agent added in the range of X mass% or more and X + 15 mass% or less obtained by the following formulas (2), (3) and (4) is applied to the hot metal bath surface stirred by the stirring blades. A method for desulfurizing hot metal, comprising adding and desulfurizing the hot metal.
Hot metal temperature: 1250 ° C or less X (mass%) = 20 (2)
Hot metal temperature: 1250 ° C and less than 1340 ° C X (mass%) = 295-0.22 x T (3)
Hot metal temperature: 1340 ℃ or higher X (mass%) = 0.2 (4)
However, in the formula (3), T is the hot metal temperature (° C.) before the desulfurization treatment.   2. The hot metal desulfurization method according to claim 1, wherein the desulfurizing agent is added to the hot metal bath surface together with a carrier gas via an upper blow lance. The upper blowing lance is arranged facing downward in the vertical direction, the inner wall radius of the processing vessel containing hot metal is D (m), and the horizontal distance from the center of the processing vessel to the center of the upper blowing lance is A (m). 3. The hot metal desulfurization according to claim 2, wherein the horizontal distance (A) is within a range satisfying the relationship of the following expression (5) with respect to the inner wall radius (D). Method.
0 ≦ A ≦ (2/3) × D… (5)

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